High-efficiency double-frame double-cutting line feed-through intermediate thickness slab production line and production method

ABSTRACT

An efficient straight through medium-heavy plate production line of double rack and double shearing line and a production method are provided. The medium-heavy plate production line comprises: a main rolling line, at least two parallel shearing lines, and straightening stacking lines that are each configured parallel outside each of the shearing lines, the main rolling line comprises: a heating furnace, a high pressure water descaling machine, a fixed width press, a stand roller, a four-roll roughing mill, an intermediate cooling device, a four-roll finishing mill, an ACC accelerated cooling device, a hot straightening machine, a  1 # labeling device and a hot segmenting shear are arranged in order, and a  1 # cooling bed, a  1 # inspection stand, a  2 # cooling bed and a  2 # inspection stand are arranged at two sides of the steel rolling and delivery rolling way; a plate turnover machine; and a traverse stand.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Phase of PCT International Application No. PCT/CN2020/118929 filed on Sep. 29, 2020, which claims benefit and priority to Chinese patent application No. CN 201910942697.7 filed on Sep. 30, 2019, the content of both are incorporated by reference herein in their entiries.

TECHNICAL FIELD

The present invention relates to a heavy plate rolling technology, particularly to an efficient straight through medium-heavy plate production line of double rack and double shearing line and a production method.

BACKGROUND ART

Medium-heavy plates are important steel and iron materials on which national economy development relies, useful in ship manufacture, building construction, bridge construction, military industry, large diameter welded pipes and so on. Currently, there are totally 76 medium-heavy plate production lines in the country, wherein 68 of them can perform efficient production, and the designed capacity is 93,740,000 tons/year. The capacity distribution of medium-heavy plates in the country is extremely unbalanced. In eastern China, northern China and central and southern areas, the capacity of medium-heavy plates is high, and part of the produced medium-heavy plate products need to be supplied to the other areas. The capacity of medium-heavy plate in north-east area can basically meet the requirement of the middle and high end market in this area, while the requirement of the low end market is supplemented by external supply. In north-west area, the market requirement on medium-heavy plates is low, and the capacity thereof is low. The capacity of medium-heavy plates in southern China and south-west areas is low, and the market requirement is met mainly by externally supplied steel plates. The capacity of medium-heavy plates in southern China and south-west areas is obviously insufficient.

Thus, there is still strong demand for enlarging the capacity of heavy plates in some areas. Since there are many production lines of heavy plates in the country, if the newly built production line still uses the previous process, layout and design, it is difficult to improve in terms of the current production scale, cost and energy consumption, and cannot be competitive in the market, thus can be limited in development.

Currently, there is no production line of heavy plates whose capacity is over 2,400,000 tons/year. The general process layout of the current production line of heavy plates mainly has the following defects:

1) The capacity scale of the rolling line and finishing line of single production line, generally no more than 2,000,000 tons, is not sufficient.

2) The layout and process of production line of heavy plates in the country are basically identical, and there is no much innovation or modification.

3) Due to the design, the slab library has too long paths, so the hot charging ratio is low (basically less than 50%).

4) The capacity of rolling line and that of the finishing line cannot be matched.

In general, the mill capacity is higher than that of the subsequent finishing line, causing that the mill capacity cannot be exerted completely.

5) The length of the rolling route is limited, and generally, the maximum length is no more than 52 m, causing low rolled piece weight and low mill capacity.

6) The rolled steel plates of heavy plates must go around the cooling bed before entering into the shearing line, so the straight-through processing of the rolled steel plates cannot be achieved.

Chinese patent CN 201410302065 discloses a method for controlling the steel plate rolling and delivery speed for production line of medium-heavy plate rolling, wherein the production line of medium-heavy plate rolling comprises in order: the last pass mill of the finishing mills, 1-N groups of delivery rolling ways after mills, pre-straightening machine, cooling controller and hot straightening machine. The method for controlling the steel plate rolling and delivery speed is an automatic speed controlling method which is integrally coordinated, comprising integrally coordinated speed control on the last pass rolling process, rolling way delivery process and pre-straightening process.

Chinese patent CN 201410302063 discloses a method for controlling temperature decrease of steel plates during the rolling production line of medium-heavy plates, relating to an automatic speed controlling method comprising rolling process of the last pass of the mill, and the rolling and delivery process that delivers steel plates from the finishing mill to the cooling control device.

SUMMARY

The objectives of the present invention is to provide an efficient straight through medium-heavy plate production line of double rack and double shearing line and a production method, which can significantly improve the efficiency for rolling, finishing and warehousing of medium-heavy plates.

To achieve the above objectives, the present invention comprises the following technical solutions:

An efficient straight-through medium-heavy plate production line of double rack and double shearing line, characterized in comprising: a main rolling line, at least two shearing lines that are configured in parallel, and straightening stacking lines that are each configured in parallel outside each of the shearing lines, wherein one of the shearing lines is arranged in a straight-through relationship with the main rolling line, in which:

the main rolling line comprises: a heating furnace, a high pressure water descaling machine, a fixed width press, a stand roller, a four-roll roughing mill, an intermediate cooling device, a four-roll finishing mill, an ACC accelerated cooling device, a hot straightening machine, 1# labeling device and a hot segmenting shear arranged along a steel rolling and delivery rolling way in order, and a 1# cooling bed, a 1# inspection stand, a 2# cooling bed and a 2# inspection stand are arranged at two sides of the steel rolling and delivery rolling way;

one of the shearing lines is arranged in a straight-through relationship with the steel rolling and delivery rolling way of the main rolling line; each of the shearing lines comprises a shearing and delivery rolling way, and, an ultrasonic flaw detector, a crop shear, a bilateral shear, a 2# labeling device, a cut-to-length shear, a 3# labeling device and a pre-stacker are arranged long the shearing and delivery rolling way in order; and, a plate turnover machine is arranged between the shearing lines;

the straightening stacking line comprises a straightening and delivery rolling way, and a cold straightening machine, a 4# labeling device and finished product collection stands at both sides of the straightening and delivery rolling way are arranged long the straightening and delivery rolling way in order; and a traverse stand is arranged between the shearing line and the straightening stacking line.

According to one example of the invention, the 1# cooling bed is arranged at one side of the steel rolling and delivery rolling way before the hot segmenting shear.

According to one example of the invention, there are at least three heating furnaces, and, a deburring machine and a weighting machine are arranged along the heating furnace rolling way in order.

According to one example of the invention, the heating furnace rolling way is arranged in a straight-through relationship with a continuous casting rolling way.

According to one example of the invention, a slab library is arranged at one side of the heating furnace, and one operation chamber is configured for the slab library and the heating furnaces; and, in the main rolling line, one operation chamber is configured for the four-roll finishing mill to the ACC accelerated cooling device.

According to one example of the invention, the two shearing lines are respectively arranged in two factory spans.

According to one example of the invention, several operation chambers for simultaneously controlling the apparatuses corresponding to the two shearing lines are arranged between the two parallel shearing lines, wherein one operation chamber is configured for the hot straightening machine, the cooling bed, the inspection stand, the ultrasonic flaw detector and the crop shear; one operation chamber is configured for the bilateral shear; and one operation chamber is configured for the cut-to-length shear, the inspection stand and the pre-stacker.

According to one example of the invention, the 1# cooling bed and the 1# inspection stand extend to the third factory span.

The present invention further provides a method for producing medium-heavy plates by using an efficient straight-through medium-heavy plate production line of double rack and double shearing line, characterized in comprising the following steps:

1) directly feeding a continuous casting slab online through a continuous casting rolling way to a heating furnace rolling way before a heating furnace at a maximum temperature, for deburring and weighting;

2) loading the weighted continuous casting slab into a heating furnace for heating according to the planned loading process;

3) after heating the continuous casting slab to a target temperature, feeding the obtained steel to a steel rolling and delivery rolling way in a main rolling line, to firstly perform surface treatment by using a high pressure water descaling machine, so as to remove iron oxide scale on the surface of the continuous casting slab;

4) feeding the continuous casting slab after high pressure water descaling to a fixed width press for online width adjustment, so as to achieve the desired width before arriving at a stand roller; then, at the time the continuous casting slab arrives at the stand roller, adjusting the plane shape, head shape, tail shape and edge shape of the continuous casting slab by the stand roller to allow good precision of width dimension of steel plate in downstream processes;

5) feeding the continuous casting slab that is conveyed out of the stand roller to a four-roll roughing roller for intermediate blank rolling, so as to roll the continuous casting slab into a specified thickness and width, or in an urgent case, into a finished product by a single rack, wherein the steel plate is not subjected to widening rolling;

6) feeding the slab that has been subjected to roughing rolling to a four-roll finishing mill to roll the slab into the desired width and thickness of steel plate according to the specified roller numbers, bite speed and reduction parameters, so as to obtain the desired plate shape and difference in the same plate, and achieve the final rolling temperature for the steel plate under different temperature control requirements;

7) after the rolling of the finished product is finished, passing the steel plate through an ACC accelerated cooling device according to the requirement on cooling control, wherein if there is a cooling requirement, performing online cooling according to the parameters such as cooling speed, flow and passing speed as modeled and specified, to achieve the target final cooling temperature, so as to improve the mechanical property of the steel plate; and if there is no cooling requirement, passing the steel plate directly through the ACC accelerated cooling device;

8) after passing the steel plate through the ACC accelerated cooling device, feeding the steel plate to a hot straightening machine by a straightening process with one pass so as to improve the plate shape, wherein if the shape of rolled plate is undesired, the number of the passes in the straightening process can be increased;

9) subjecting the steel plate that has been treated by the hot straightening machine to an intermediate process labeling at 1# labeling device so as to facilitate the tracing of the intermediate process of the steel plate;

10) segmenting the labeled steel plate at a hot segmenting shear so as to meet the requirement on the maximum length for entering into a cooling bed, wherein the segmented steel plate can be cooled by selecting different cooling beds according to the stream flow condition; and the steel plate for straight-through processing can be directly fed into a shearing rolling way of the shearing line from the delivery rolling way, without entering into the cooling bed;

11) sending the cooled steel plate to one of the two inspection stands for inspection and delivering it to the shearing rolling way of the shearing line;

12) feeding the steel plate which has been passed through the inspection stand (the temperature has been reduced to be below 80° C.) to a flaw detector to perform flaw detecting operation according to the different requirements on flaw detecting, wherein the steel plate that needs no flaw detecting is passed directly through the flaw detector;

13) feeding the steel plate which has finished the flaw detecting operation to a crop shear for head and tail cutting, so as to cut a “tongue” part of the head, and segment for a length of over 30 m, wherein the segmentation length is adjusted according to the length of the rolling way; and wherein the steel plate segmentation is prepared and ready for later edge shearing; and if the tail shape of the steel plate is undesired, the tail cutting treatment must be performed;

14) feeding the steel plate which has been subjected to the head and tail cutting to a bilateral shear for cutting burrs on two sides of the steel plate, wherein the location of the movable shear of the bilateral shear is adjusted in advance according to the width of the finished product to be cut;

15) after cutting by the bilateral shear, subjecting the steel plate to a sample jet printing at a labeling device, wherein if there is no sample of the steel plate, the labeling device is omitted;

16) after the steel plate is passed through the labeling device, feeding the steel plate to a cut-to-length shear to cut the steel plate into a length meeting the requirement of the final contract, and to perform sampling according to the requirement on sampling the steel plate, and sending the sampled big sample to a sample shear for the next processing and property testing;

17) after cutting the finished product of the steel plate, feeding it to an inkjet printer to perform jet printing on the finished product, so as to print contract information, type of steel, ship classification society logo and required information on flaw detecting onto the steel plate, wherein if the shape of the steel plate is undesired, only the plate number is printed, and the steel plate is later passed through a traverse stand for a cold correction printing; and if turnover is needed, the steel plate is traversed to a plate turnover machine for a turnover inspection; and

18) after finishing the jet printing, sending the steel plate to a final product inspection site for inspection, wherein if the steel plate has no problem after inspection, it is directly passed through a pre-stacker and enters into a library through the rolling way for stacking; and if the shape of the steel plate is undesired, it is passed through the traverse stand to enter into a cold straightening machine for shape correction, and labeling by a labeling device after correction; and, the labeled steel plate enters into a library of finished products through a delivery rolling way, and enters into a stacking location of the library of finished products for stacking through a collection stand for finished products according to the requirement on stacking, to wait to be shipped out of the factory.

According to one example of the invention, after step 5), if there is a requirement of temperature controlling and finish rolling on the slab, an intermediate cooling device is used to perform water spray cooling after rough rolling, wherein the parameters such as flow and speed can be calculated according to the cooling model to achieve the function of temperature control of slab of different requirements, and part of the slabs without temperature control requirement can be passed directly through the intermediate cooling device.

Beneficial Effects

1. The production line layout and production method of the present invention can obtain a production scale of 3,000,000 tons/year, with improved production efficiency and reduced production cost.

2. The present invention uses an ultra-long rolling, and can achieve a yield of ≥94%.

3. The production line layout of the present invention is reasonable and beneficial for combining operation chambers. There are can be 8 operation chambers at minimum arranged in the main line to reduce the number of the operators, which can improve the productivity by more than 50%.

4. The slab is conveyed straight-through the heating furnace zone, so that the hot charging rate can be no less than 60%.

5. The processing layout of the present invention can be easily overhauled, and the spare parts for each of the unit equipments can be conveniently sent to or out of the factory. The production line of the present invention only occupies three factory spans, which has a small footprint and a high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, properties and advantages of the present invention will become more apparent when the following detailed description of the disclosure is read with reference to the accompanying drawings and examples, and the same reference signs in the drawings always refer to the same features, in which:

FIG. 1 is a schematic view 1 of the process layout according to the inventive example 1.

FIG. 2 is a schematic view 2 of the process layout according to the inventive example 1.

FIG. 3 is a schematic view 1 of the process layout according to the inventive example 2.

FIG. 4 is a schematic view 2 of the process layout according to the inventive example 2.

DETAILED DESCRIPTION

To more clearly illustrate the technical solutions and advantages of the present invention, the specific embodiments are described with reference to the accompanying drawings. The specific embodiments are only to explain the present invention, not to limit the present invention in any way.

Referring to FIGS. 1-2, an efficient straight through medium-heavy plate production line of double rack and double shearing line of the present invention comprises: a main rolling line L, two parallel shearing lines C1, C2, and straightening stacking lines S1, S2 arranged respectively parallel outside each of the shearing lines C1, C2, wherein one of the shearing lines, C1, is arranged in a straight-through relationship with the main rolling line L, in which:

the main rolling line L comprises: a heating furnace 1, a high pressure water descaling machine 2, a fixed width press 3, a stand roller 4, a four-roll roughing mill 5, an intermediate cooling device 6, a four-roll finishing mill 7, an ACC accelerated cooling device 8, a hot straightening machine 9, a 1# labeling device 10 and a hot segmenting shear 11 arranged along a steel rolling and delivery rolling way in order, and a 1# cooling bed 12, a 1# inspection stand 13, a 2# cooling bed 14 and a 2# inspection stand 15 are respectively arranged at two sides of the steel rolling and delivery rolling way;

each of the shearing lines C1 (taking shearing line C1 as an example) comprises a shearing and delivery rolling way, and an ultrasonic flaw detector 16, a crop shear 17, a bilateral shear 18, a 2# labeling device 19, a cut-to-length shear 20, a 3# labeling device 21 and a pre-stacker 22 are arranged long the shearing and delivery rolling way in order; and, a plate turnover machine 23 is arranged between the shearing lines C1, C2;

the straightening stacking line S1 (taking straightening stacking line S1 as an example) comprises a straightening and delivery rolling way, and a cold straightening machine 24 and a 4# labeling device 25 and finished product collection stands 26, 26′ at both sides of the straightening and delivery rolling way are arranged long the straightening and delivery rolling way in order; and

a traverse stand 27 is arranged between the shearing line C1 and the straightening stacking line S1.

Preferably, there are at least three heating furnaces 1, and a deburring machine 28 and a weighting machine 29 are arranged along the heating furnace rolling ay in order. Preferably, the heating furnace rolling way is arranged in a straight-through relationship with a continuous casting rolling way.

Referring to FIGS. 3-4, the 1# cooling bed 12 of the present invention is arranged on one side of the steel rolling and delivery rolling way before the hot segmenting shear 11, that is, the 1# cooling bed 12 and the 1# inspection stand 13 are separately arranged; part of the steel plates which need to be stacked and cooled may be directly disposed at the empty space between the 1# inspection stand and 1# cooling bed, thus, the natural zone for temperature keeping, stacking and cooling formed between the 1# inspection stand and the 1# cooling bed can be used to improve the stacking and cooling effect of steel plates; and, moreover, such a layout is also beneficial for slowing down the stream flow at the junction between the steel rolling at the cooling bed and the finishing line, since there is a bigger buffering zone of steel plates, which is beneficial for improving capacity.

Preferably, a slab library is arranged at one side of the heating furnace, and one operation chamber is configured for the slab library and the heating furnaces; and, in the main rolling line, one operation chamber is configured for the four-roll finishing mill to the ACC accelerated cooling device.

Preferably, several operation chambers for simultaneously controlling the apparatuses corresponding to the two shearing lines are arranged between the two parallel shearing lines, wherein one operation chamber is configured for the hot straightening machine, the cooling bed, the inspection stand, the ultrasonic flaw detector and the crop shear; one operation chamber is configured for the bilateral shear; and one operation chamber is configured for the cut-to-length shear, the inspection stand and the pre-stacker.

A method for producing a medium-heavy plates by using an efficient straight through medium-heavy plate production line of double rack and double shearing line of the present invention comprises the following steps:

1) directly feeding a continuous casting slab online through a continuous casting rolling way to a heating furnace rolling way before a heating furnace 1 at maximum temperature for deburring and weighting;

2) loading the weighted continuous casting slab into the heating furnace 1 for heating according to the planned loading process;

3) after heating the continuous casting slab to a target temperature, feeding the obtained steel to a steel rolling and delivery rolling way in a main rolling line, to firstly perform surface treatment by using a high pressure water descaling machine 2, so as to remove iron oxide scale on the surface of the continuous casting slab;

4) feeding the continuous casting slab after high pressure water descaling to a fixed width press 3 for online width adjustment, so as to achieve the desired width before arriving at a stand roller; then, at the time the continuous casting slab arrives at the stand roller 4, adjusting the plane shape, head shape, tail shape and edge shape of the continuous casting slab by the stand roller 4 to allow good precision of width dimension of steel plate in downstream processes;

5) feeding the continuous casting slab that is conveyed out of the stand roller to a four-roll roughing roller 5 for intermediate blank rolling, so as to roll the continuous casting slab into a specified thickness and width, or in an urgent case, into a finished product by a single rack, wherein the steel plate is not subjected to widening rolling;

6) feeding the slab that has been subjected to roughing rolling to a four-roll finishing mill 7 to roll the slab into the desired width and thickness of steel plate according to the specified roller numbers, bite speed and reduction parameters, so as to obtain the desired plate shape and difference in the same plate, and achieve the final rolling temperature for the steel plate under different temperature control requirements;

7) after the rolling of the finished product is finished, passing the steel plate through an ACC accelerated cooling device 8 according to the requirement on cooling control, wherein if there is a cooling requirement, performing online cooling according to the parameters such as cooling speed, flow and passing speed as modeled and specified, to achieve the target final cooling temperature, so as to improve the mechanical property of the steel plate; and if there is no cooling requirement, passing the steel plate directly through the ACC accelerated cooling device 8;

8) after passing the steel plate through the ACC accelerated cooling device, feeding the steel plate to a hot straightening machine 9 by a straightening process with one pass so as to improve the plate shape, wherein if the shape of rolled plate is undesired, the number of the passes in the straightening process can be increased;

9) subjecting the steel plate that has been treated by the hot straightening machine to an intermediate process labeling at 1# labeling device 10 so as to facilitate the tracing of the intermediate process of the steel plate;

10) segmenting the labeled steel plate at a hot segmenting shear 11 so as to meet the requirement on the maximum length for entering into a cooling bed, wherein the segmented steel plate can be cooled by selecting different cooling beds 12, 14 according to the stream flow condition; and the steel plate for straight-through processing can be directly fed into a shearing rolling way of the shearing line from the delivery rolling way, without entering into the cooling bed;

11) sending the cooled steel plate to one of the two inspection stands 13, 15 for inspection and delivering it to the shearing rolling way of the shearing line;

12) feeding the steel plate which has been passed through the inspection stands 13, 15 (the temperature has been reduced to be below 80° C.) to a flaw detector 16 to perform flaw detecting operation according to the different requirements on flaw detecting, wherein the steel plate that needs no flaw detecting is passed directly through the flaw detector 16;

13) feeding the steel plate which has finished the flaw detecting operation to a crop shear 17 for head and tail cutting, so as to cut a “tongue” part of the head, and segment for a length of over 30 m, wherein the segmentation length is adjusted according to the length of the rolling way; and wherein the steel plate segmentation is prepared and ready for later edge shearing; and if the tail shape of the steel plate is undesired, the tail cutting treatment must be performed;

14) feeding the steel plate which has been subjected to the head and tail cutting to a bilateral shear 18 for cutting burrs on two sides of the steel plate, wherein the location of the movable shear of the bilateral shear 18 is adjusted in advance according to the width of the finished product to be cut;

15) after cutting by the bilateral shear 18, subjecting the steel plate to a sample jet printing at a labeling device 19, wherein if there is no sample of the steel plate, the labeling device is omitted;

16) after the steel plate is passed through the labeling device, feeding the steel plate to a cut-to-length shear 20 to cut the steel plate into a length meeting the requirement of the final contract, and to perform sampling according to the requirement on sampling the steel plate, and sending the sampled big sample to a sample shear for the next processing and property testing;

17) after cutting the finished product of the steel plate, feeding it to an inkjet printer to perform jet printing on the finished product, so as to print contract information, type of steel, ship classification society logo and required information on flaw detecting onto the steel plate, wherein if the shape of the steel plate is undesired, only the plate number is printed, and the steel plate is later passed through a traverse stand 27 for a cold correction printing; and if turnover is needed, the steel plate is traversed to a plate turnover machine 23 for a turnover inspection; and

18) after finishing the jet printing, sending the steel plate to a final product inspection site for inspection, wherein if the steel plate has no problem after inspection, it is directly passed through a pre-stacker 22 and enters into a library through the rolling way for stacking; and if the shape of the steel plate is undesired, it is passed through the traverse stand 27 to enter into a cold straightening machine 24 for shape correction, and labeling by a labeling device 25 after correction; and, the labeled steel plate enters into a library of finished products through a delivery rolling way, and enters into a stacking location of the library of finished products for stacking through a collection stand 26 for finished products according to the requirement on stacking, to wait to be shipped out of the factory.

Preferably, after step 5), if there is a requirement of temperature controlling and finish rolling on the slab, the intermediate cooling device 6 is used to perform water spray cooling after rough rolling, wherein the parameters such as flow and speed can be calculated according to the cooling model to achieve the function of temperature control of slabs of different requirements, and part of the slabs without temperature control requirement can be passed directly through the intermediate cooling device 6.

Examples

1) A Q345qD slab, with a thickness of 250 mm, a width of 2200 mm, a length of 8000 mm and a weight of 34.54 t was sent from a continuous casting rolling way to a rolling way of a heating furnace of heavy plates. After being treated by a deburring machine, it was loaded into a 1# heating furnace 1 for heating, wherein the temperature for loading the steel plate was 600° C., a target heating temperature was 1080° C., and the actual tapping temperature was 1085° C.

2) The steel plate conveyed out of the furnace was sent to a high pressure water descaling machine 2, wherein the descaling pressure was 210 bar, and the descaling speed was 1.2 m/s, and the water consumption for each group of nozzles was 290 m³/h.

3) The steel plate was passed through a fixed width press 3, wherein the width was adjusted to 50 mm by side pressure.

4) Rolling by a stand roller: the plate was rolled 1 pass by a stand roller 4, wherein the rolling force was 100 t, and the rolling speed was 2 m/s.

5) Rolling by a roughing mill: the temperature of the steel plate measured at the inlet of the roughing mill was 1030° C., and the steel plate was transferred through 9 passes, and the thickness of the transferred steel plate by rolling was from 250 mm to 76 mm, wherein the rolling speed was 2 m/s, the maximum rolling force was 6300 t, and the maximum torque was 3000 kNm.

6) Intermediate cooling: the temperature of the steel plate was reduced to 880° C. by the intermediate cooling, and transferred to a finishing mill 7 for rolling.

7) Rolling by a finishing mill: when the temperature of the steel plate was measured to be 880° C. at the inlet of the finishing mill 7, the steel plate was rolled through 9 passes, with 8 passes with loading, and the last pass was passed through; the rolling speed for the first 6 passes was 7 m/s, and the rolling speed for the last pass was 4 m/s; the maximum reduction was 20 mm; the reduction rate of the last pass with loading was 10%; the final rolling temperature of the steel plate was 780° C.; the rolling size of the steel plate was 20×2150×102300 mm; and, the rolled steel plate was transferred to ACC for cooling.

8) ACC cooling process: the cooling rate was 15° C./min, the cooling start temperature was 780° C., and the final cooling temperature was 540° C.; and, the cooled steel plate was sent to a hot straightening machine 9 for straightening.

9) Hot straightening process: one straightening roller was used, wherein the straightening force was 300 t, the roll gap was 19.5 mm, and the straightening speed was 2.5 m/s.

10) Jet printing: the steel plate was subjected to jet printing by a hot straightening machine 9 with a board number of the day (29A01130000), indicating big plate No. 130 on Oct. 1, 2019.

11) The steel plate was segmented at a hot segmenting shear 11. The two segmented steel plates had a length of 48 m and 47.6 m, respectively, and entered into 1# cooling bed 12 and 2# cooling bed 14.

12) Two sub-plates were respectively passed through 1# inspection stand 13 and 2# inspection stand 15 by cooling bed traverse so that the temperature was reduced to be below 80° C., and then transferred to 1# flaw detector and 2# flaw detector for flaw detecting, wherein the speed for flaw detecting was 0.3 m/s-1 m/s.

13) After flaw detecting, the steel plates were sent to 1# crop shear and 2# crop shear so that the round corneredhead and tail ends were cut, and the rough cutting was performed to produce 4 steel plates, wherein the lengths were 23500 mm (steel plate 1), 23500 mm (steel plate 2), 23000 mm (steel plate 3) and 29000 mm (steel plate 4), respectively.

14) The segmented steel plates were sent to 1# bilateral shear and 2# bilateral shear for edge cutting, wherein the shear edge clearance was set to be 2.0 mm, the shear frequency was at most 30 times/min, and the shear step was 1300 mm/1500 mm. Two sides of the sheared steel plates had slightly different trim amounts according to sickle bend condition of the steel plates, wherein the widths of four sheared steel plates were 2051 mm, 2049 mm, 2050 mm and 2050 mm, and the steel plate was passed through the later sample jet printer.

15) The steel plates were subjected to sample number labeling at 3# labeling device 21, and the remaining steel plates were passed through the sample jet printer.

16) 1# cut-to-length shear and 2# cut-to-length shear were used according to the contract length to cut the steel plates into finished products with a length of 14500 mm, 9000 mm, 12500 mm, 11000 mm, 12000 mm, 11000 mm, 12000 mm and 16880 mm. One big sample with a length of 120 mm was sent to a processing operation chamber for sample processing and property testing.

17) After cut-to-length cutting, the steel plate was sent to 4# labeling device 25 or 5# labeling device for jet printing on the finished product, so as to print the information such as contract dimension, steel plate trademark, weight, requirement on flaw detecting and ship classification society logo onto the steel plate, wherein due to the shape of the steel plates, steel plates 1, 2 were passed through the labeling device without operation.

18) Upon inspection, the surface, appearance and jet printing of six small plates are qualified, so they were sent to 1# pre-stacker and 2# pre-stacker 22 for stacking, and then through 3# and 5# collection stand 26 for finished products for warehousing and stacking, wherein the shape of two plates was undesired, so they were sent to 1# straightening machine and 2# straightening machine through 1# and 3# traverse stand 27 for plate shape correction; and, after straightening, these two steel plates were subjected to the final jet printing of finished product at 6# and 7# labeling devices, and sent to a library of finished products through 4# and 6# collection stands for finished products for stacking.

Although the specific embodiments of the present invention have been described, those skilled in the art will understand that these are just illustrative, and the protection scope of the present invention is defined by the accompanying claims. Various changes or modifications to the invention can be made by those skilled in the art after reading the above teachings of the invention, and these equivalent variations fall in the scope defined by the accompanying claims of the application as well. 

1. An efficient straight through medium-heavy plate production line of double rack and double shearing line, characterized in comprising: a main rolling line, at least two shearing lines that are configured in parallel, and straightening stacking lines that are each configured in parallel outside each of the shearing lines, wherein one of the shearing lines is arranged in a straight-through relationship with the main rolling line, in which: the main rolling line comprises: a heating furnace, a high pressure water descaling machine, a fixed width press, a stand roller, a four-roll roughing mill, an intermediate cooling device, a four-roll finishing mill, an ACC accelerated cooling device, a hot straightening machine, 1# labeling device and a hot segmenting shear arranged along a steel rolling and delivery rolling way in order, and a 1# cooling bed, a 1# inspection stand, a 2# cooling bed and a 2# inspection stand are respectively arranged at two sides of the steel rolling and delivery rolling way; one of the shearing lines is arranged in a straight-through relationship with the steel rolling and delivery rolling way of the main rolling line; each of the shearing lines comprises a shearing and delivery rolling way, and an ultrasonic flaw detector, a crop shear, a bilateral shear, a 2# labeling device, a cut-to-length shear, a 3# labeling device and a pre-stacker are arranged long the shearing and delivery rolling way in order; and, a plate turnover machine is arranged between the shearing lines; the straightening stacking line comprises a straightening and delivery rolling way, and a cold straightening machine, a 4# labeling device and finished product collection stands at both sides of the straightening and delivery rolling way are arranged long the straightening and delivery rolling way in order; and a traverse stand is arranged between the shearing line and the straightening stacking line.
 2. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1, wherein the 1# cooling bed is arranged at one side of the steel rolling and delivery rolling way before the hot segmenting shear.
 3. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1, wherein there are at least three heating furnaces, and a deburring machine and a weighting machine are arranged along the heating furnace rolling way in order.
 4. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 3, wherein the heating furnace rolling way is arranged in a straight-through relationship with a continuous casting rolling way.
 5. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1, wherein a slab library is arranged at one side of the heating furnaces, and one operation chamber is configured for the slab library and the heating furnaces; and, in the main rolling line, one operation chamber is configured for the four-roll finishing mill to the ACC accelerated cooling device.
 6. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1, wherein the two shearing lines are respectively arranged in two factory spans.
 7. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1 or 6, wherein several operation chambers for simultaneously controlling the apparatuses corresponding to the two shearing lines are arranged between the two parallel shearing lines, wherein one operation chamber is configured for the hot straightening machine, the cooling bed, the inspection stand, the ultrasonic flaw detector and the crop shear; one operation chamber is configured for the bilateral shear; and one operation chamber is configured for the cut-to-length shear, the inspection stand and the pre-stacker.
 8. The efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1, 2 or 6, wherein the 1# cooling bed and the 1# inspection stand extend to the third factory span.
 9. A method for producing medium-heavy plates by using an efficient straight through medium-heavy plate production line of double rack and double shearing line according to claim 1, comprising the following steps: 1) directly feeding a continuous casting slab online through a continuous casting rolling way to a heating furnace rolling way before a heating furnace at maximum temperature for deburring and weighting; 2) loading the weighted continuous casting slab into a heating furnace for heating according to the planned loading process; 3) after heating the continuous casting slab to a target temperature, feeding the obtained steel to a steel rolling and delivery rolling way in a main rolling line, to firstly perform surface treatment by using a high pressure water descaling machine, so as to remove iron oxide scale on the surface of the continuous casting slab; 4) feeding the continuous casting slab after high pressure water descaling to a fixed width press for online width adjustment, so as to achieve the desired width before arriving at a stand roller; then, at the time the continuous casting slab arrives at the stand roller, adjusting the plane shape, head shape, tail shape and edge shape of the continuous casting slab by the stand roller for to allow good precision of width dimension of steel plate in downstream processes; 5) feeding the continuous casting slab that is conveyed out of the stand roller to a four-roll roughing roller for intermediate blank rolling, so as to roll the continuous casting slab into a specified thickness and width, or in an urgent case, into a finished product by a single rack, wherein the steel plate is not subjected to widening rolling; 6) feeding the slab that has been subjected to roughing rolling to a four-roll finishing mill to roll the slab into the desired width and thickness of the steel plate according to the specified roller numbers, bite speed and reduction parameters, so as to obtain the desired plate shape and difference in the same plate, and achieve the final rolling temperature for the steel plate under different temperature control requirement; 7) after the rolling of the finished product is finished, passing the steel plate through an ACC accelerated cooling device according to the requirement on cooling control, wherein if there is a cooling requirement, performing online cooling according to the parameters such as cooling speed, flow and passing speed as modeled and specified, to achieve the target final cooling temperature, so as to improve the mechanical property of the steel plate; and if there is no cooling requirement, passing the steel plate directly through the ACC accelerated cooling device; 8) after passing the steel plate through the ACC accelerated cooling device, feeding the steel plate to a hot straightening machine by a straightening process with one pass so as to improve the plate shape, wherein if the shape of rolled plate is undesired, the number of the passes in the straightening process can be increased; 9) subjecting the steel plate that has been treated by the hot straightening machine to an intermediate process labeling at 1# labeling device so as to facilitate the tracing of the intermediate process of the steel plate; 10) segmenting the labeled steel plate at a hot segmenting shear so as to meet the requirement on the maximum length for entering into a cooling bed, wherein the segmented steel plate can be cooled by selecting different cooling beds according to the stream flow condition; and the steel plate for straight-through processing can be directly fed into a shearing rolling way of the shearing line from the delivery rolling way, without entering into the cooling bed; 11) sending the cooled steel plate to one of the two inspection stands for inspection and delivering it to the shearing rolling way of the shearing line; 12) feeding the steel plate which has been passed through the inspection stand (the temperature has been reduced to be below 80° C.) to a flaw detector to perform flaw detecting operation according to the different requirements on flaw detecting, wherein the steel plate that needs no flaw detecting is passed directly through the flaw detector; 13) feeding the steel plate which has finished the flaw detecting operation to a crop shear for head and tail cutting, so as to cut a “tongue” part of the head, and segment for a length of over 30 m, wherein the segmentation length is adjusted according to the length of the rolling way; and wherein the steel plate segmentation is prepared and ready for later edge shearing; and if the tail shape of the steel plate is undesired, the tail cutting treatment must be performed; 14) feeding the steel plate which has been subjected to the head and tail cutting to a bilateral shear for cutting burrs on two sides of the steel plate, wherein the location of the movable shear of the bilateral shear is adjusted in advance according to the width of the finished product to be cut; 15) after cutting by the bilateral shear, subjecting the steel plate to sample jet printing at a labeling device, wherein if there is no sample of the steel plate, the labeling device is omitted; 16) after the steel plate is passed through the labeling device, feeding the steel plate to a cut-to-length shear to cut the steel plate into a length meeting the requirement of the final contract, and to perform sampling according to the requirement on sampling the steel plate, and sending the sampled big sample to a sample shear for the next processing and property testing; 17) after cutting the finished product of the steel plate, feeding it to an inkjet printer to perform jet printing on the finished product, so as to print contract information, type of steel, ship classification society logo and required information on flaw detecting onto the steel plate, wherein if the shape of the steel plate is undesired, only the plate number is printed, and the steel plate is later passed through a traverse stand for a cold correction printing; and if turnover is needed, the steel plate is traversed to a plate turnover machine for a turnover inspection; and 18) after finishing the jet printing, sending the steel plate to a final product inspection site for inspection, wherein if the steel plate has no problem after inspection, it is directly passed through a pre-stacker and enters into a library through the rolling way for stacking; and if the shape of the steel plate is undesired, it is passed through the traverse stand to enter into a cold straightening machine for shape correction, and labeling by a labeling device after correction; and, the labeled steel plate enters into a library of finished products through a delivery rolling way, and enters into a stacking location of the library of finished products for stacking through a collection stand for finished products according to the requirement on stacking, to wait to be shipped out of the factory.
 10. The method according to claim 9, wherein after step 5), if there is a requirement of temperature controlling and finish rolling on the slab, an intermediate cooling device is used to perform water spray cooling after rough rolling, wherein the parameters such as flow and speed can be calculated according to the cooling model to achieve the function of temperature control of slabs of different requirements, and part of the slab without temperature control requirement can be passed directly through the intermediate cooling device. 